This invention relates to a test procedure for the testing of underground or otherwise inaccessible liquid storage tanks for leakage, particulary a tank that is not readily susceptible to visual inspection, typically a buried fuel storage tank of a filling station, and to equipment for carrying out this test procedure.
Conventionally, fuel storage tanks in the U.K. must, by regulation, be tested for leakage at stipulated periods to secure a licence for use from the local licensing authority. Current legislation in the U.K. requires that if leakage should be detected at a rate exceeding 380 millilitres per hour, then the tank must be taken out of service, for repair. The officially recommended test requires (i) removal of the fuel--petrol or diesel--(ii) cleaning the tank, (iii) filling the tank with water, (iv) applying an air pressure for a prescribed period, (v) thereafter determining any loss of pressure, which would indicate leakage, and (vi) removal and disposal of the now contaminated water by a licensed operator. Consequently, the tank is non-operational for a considerable period. With a view to providing an improved technique, and in particular one that most advantageously does not require removal of the fuel involved, or the wastage and disposal of thousands of gallons of contaminated water, various computer based methods and apparatus have been evolved, but these are understandably relatively expensive and usually require highly specialised and trained operatives.